Preparation method of iron phosphate

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, in particular to a preparation method of iron phosphate. Comprising the following steps: respectively carrying out impurity removal treatment on rutile mother liquor and crude phosphoric acid by taking silicon-containing waste alkali liquor as an alkaline impurity removal agent to obtain ferric salt and phosphorus salt, and then reacting the ferric salt, the phosphorus salt and hydrogen peroxide to prepare the iron phosphate. According to the method, the rutile mother liquor and the crude phosphoric acid are subjected to impurity removal through the silicon-containing waste alkali liquor to obtain the iron salt and the phosphorus salt for the battery-grade iron phosphate, the treatment cost of the rutile mother liquor and the crude phosphoric acid is reduced, the impurity content of the obtained iron salt and the phosphorus salt is lower, and compared with an existing method, the silicon-containing waste alkali liquor is adopted for replacing alkali liquor, so that the production cost of the iron phosphate can be reduced; meanwhile, the purification effect of ferric salt and phosphorus salt can be improved, the quality of ferric phosphate is improved, meanwhile, recycling of the silicon-containing waste alkali liquid is achieved, and environmental pollution and waste alkali liquid treatment burden are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a method for preparing iron phosphate. Background Art

[0002] In recent years, lithium iron phosphate has been significantly developed as an important positive electrode material for lithium-ion batteries. As a precursor of lithium iron phosphate, the morphology, structure, particle size and purity of iron phosphate have a key influence on the performance of lithium iron phosphate. Therefore, the pH of the entire iron phosphate reaction process needs to be precisely controlled; the production of one ton of iron phosphate requires about 1.5 tons of liquid alkali solution or about 0.8 tons of ammonia water, which greatly increases the production cost; in addition, if ammonia water is used to adjust the pH, it will also lead to the generation of ammonia nitrogen wastewater, which requires further treatment.

[0003] In the past two years, the profit margin of iron phosphate has been continuously compressed due to the increase in the prices of raw and auxiliary materials and the decline in the price of iron phosphate. Therefore, it is necessary to further optimize the synthesis process of iron phosphate and reduce the production cost of iron phosphate.

[0004] In industrial production, a large amount of silicon-containing waste alkali liquid is often produced, such as zirconium industry waste alkali liquid produced in the zirconium oxychloride process. At present, most of the silicon-containing waste alkali liquid is directly discharged or simply treated by neutralization method. These treatment methods not only cause serious harm to the environment, but also increase the input of acid and increase production costs. If this part of waste alkali liquid can be used to prepare iron phosphate, it will be of great significance to reduce the production cost of iron phosphate and the treatment cost of waste alkali liquid as well as environmental protection.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing ferric phosphate to solve the technical problems in the prior art that the production cost of ferric phosphate is high and silicon-containing waste alkali liquid is not reasonably utilized. The present invention uses silicon-containing waste alkali liquid in the production of ferric phosphate, which can not only reduce the production cost of ferric phosphate, but also improve the quality of ferric phosphate. At the same time, it can avoid environmental pollution caused by silicon-containing waste alkali liquid, and reduce the treatment burden and cost of silicon-containing waste alkali liquid.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] A method for preparing ferric phosphate comprises the following steps:

[0009] The silicon-containing waste alkali liquid is used as an alkaline impurity remover to remove impurities from rutile mother liquor and crude phosphoric acid respectively to obtain iron salt and phosphate salt, and then the iron salt and the phosphate salt are reacted with hydrogen peroxide to prepare iron phosphate.

[0010] Preferably, the method for preparing the ferric phosphate specifically comprises the following steps:

[0011] S1. Add the silicon-containing waste alkali solution to the rutile mother liquor to adjust the pH to 4-5 to precipitate the impurity ions. After solid-liquid separation, add acid to the filtrate to adjust the pH to 1.8-2.0 to obtain the iron salt;

[0012] S2. Add the silicon-containing waste alkali solution to the crude phosphoric acid to adjust the pH to 2-3, then add alkali to adjust the pH to 4.3-4.8, precipitate the impurity ions, separate the solid and liquid, continue to add the alkali to the filtrate, adjust the pH to 6-8, and obtain the phosphate salt;

[0013] S3. using the iron salt, the phosphate salt and the hydrogen peroxide to carry out a precipitation reaction, solid-liquid separation and washing to obtain a washed filter cake;

[0014] S4. Slurrying the first-wash filter cake, adding phosphoric acid to the slurry, heating to perform aging and crystallization reaction, washing after solid-liquid separation to obtain a second-wash filter cake, and calcining the second-wash filter cake to obtain anhydrous iron phosphate.

[0015] Preferably, in step S1, the mass concentration of NaOH in the silicon-containing waste alkali liquid is 5%-10%, and the mass concentration of Si is 0.25%-0.5%.

[0016] Preferably, in step S1, the acid includes phosphoric acid and / or sulfuric acid.

[0017] Preferably, in step S1, the mass concentration of ferrous ions in the iron salt is 40-90 g / L.

[0018] Preferably, in step S2, in the crude phosphoric acid, the P2O5 content is 50wt% to 55wt%, the F content is 0.2wt% to 0.3wt%, the Fe content is 0.5wt% to 0.8wt%, the Ca content is 0 to 0.05wt%, the Mg content is 0.5wt% to 0.8wt%, the Mn content is 0 to 0.05wt%, the Al content is 0.1wt% to 0.3wt%, and the Ti content is 0.05wt% to 0.15wt%.

[0019] Preferably, in step S2, the mass concentration of NaOH in the silicon-containing waste alkali liquid is 10%-20%, and the mass concentration of Si is 0.5%-1%.

[0020] Preferably, in step S2, the alkali includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0021] Preferably, in step S2, the mass percentage of phosphorus element in the phosphorus salt is 2%-4%.

[0022] Preferably, in step S3, the molar ratio of Fe, P, H2O2 in the iron salt, the phosphate salt and the hydrogen peroxide is 1-1.3:1:0.5-1.

[0023] Preferably, in step S4, after adding the phosphoric acid, the pH of the slurry is 1.4-1.6.

[0024] Preferably, in step S4, the temperature of the aging-transcrystal transformation reaction is 85-95° C., and the time of the aging-transcrystal transformation reaction is 1-3 h.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention utilizes silicon-containing waste alkali liquid to remove impurities from rutile mother liquor and crude phosphoric acid to obtain iron salt and phosphoric acid for battery-grade iron phosphate, thereby reducing the processing cost of rutile mother liquor and crude phosphoric acid, and improving the impurity removal effect of iron salt and phosphoric acid, while also reducing the processing cost of silicon-containing waste alkali liquid and the harm to the environment; this method can not only reduce the production cost of iron phosphate, but also improve the quality of iron phosphate.

[0027] (2) Since the silicon-containing waste alkali liquid contains a large amount of silicon, when the rutile mother liquor is adjusted to the corresponding pH during the impurity removal process, silicic acid will be formed. Its colloid particles are negatively charged and can flocculate with positively charged colloid particles (such as iron hydroxide) to form a precipitate, making the impurity removal effect better than using only sodium hydroxide, and the prepared battery-grade iron phosphate has fewer impurities.

[0028] (3) Since waste alkali liquor contains a large amount of silicon and crude phosphoric acid contains F, Ca, Mg, Fe, Mn, Al and other elements, when waste alkali liquor is added to adjust the pH during the crude acid purification process, when the pH is initially low, silicate reacts with F. - Reaction to generate SiF6 2- Or SiF4 gas, and SiF6 2- It is easy to form precipitation with other metal ions. As the pH increases, silicate and H + The reaction generates silica precipitate; then alkali is added to adjust the pH to completely precipitate Ti. The use of silicon-containing waste alkali liquid in combination with alkali to remove impurities from crude phosphoric acid is more effective than using alkali alone for impurity removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1The scanning electron microscope images are of the iron phosphate prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0031] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0032] The present invention provides a method for preparing iron phosphate, comprising the following steps:

[0033] The silicon-containing waste alkali liquid is used as an alkaline impurity remover to remove impurities from rutile mother liquor and crude phosphoric acid respectively to obtain iron salt and phosphate salt, and then the iron salt and the phosphate salt are reacted with hydrogen peroxide to prepare iron phosphate.

[0034] At present, liquid alkali or ammonia water is usually used to remove impurities from raw materials during the production of ferric phosphate, which is costly and will also produce ammonia nitrogen wastewater when ammonia water is used. In view of the above problems, the present invention uses silicon-containing waste alkali liquid to remove impurities from rutile mother liquor and crude phosphoric acid, and uses the iron salt and phosphate salt after impurities removal to prepare ferric phosphate, which can significantly reduce the treatment cost of iron salt and phosphate salt, thereby reducing the production cost of ferric phosphate; at the same time, the silicon-containing waste alkali liquid is reused, reducing the treatment cost of the silicon-containing waste alkali liquid and the harm to the environment.

[0035] In the process of removing impurities from rutile mother liquor, when alkali is added to adjust the pH to remove Al and Ti, part of the trivalent iron will form ferric hydroxide, which is difficult to remove with conventional alkali. However, because the silicon-containing waste alkali liquid contains silicon, silicic acid will be formed at the corresponding pH. Its colloid particles are negatively charged and can flocculate with positively charged colloid particles (such as ferric hydroxide) to form a precipitate, making the impurity removal effect better than using only sodium hydroxide, and the prepared battery-grade iron phosphate has fewer impurities.

[0036] Crude phosphoric acid contains F, Ca, Mg, Fe, Mn, Al and other elements. Since silicon-containing waste alkali liquid contains a large amount of silicon, when silicon-containing waste alkali liquid is added to adjust the pH during the purification of crude phosphoric acid, when the pH is low at the beginning, silicate reacts with F. - Reaction to generate SiF6 2- Or SiF4 gas, and SiF6 2- It is easy to form precipitation with other metal ions, which can remove metal ions and fluoride ions. Continuing to add alkali to adjust the pH can completely precipitate Al and Ti.

[0037] From the above discussion, it can be seen that using silicon-containing waste alkali liquor as an alkaline impurity remover to remove impurities from rutile mother liquor and crude phosphoric acid can not only reduce the production cost of ferric phosphate and the treatment cost of silicon-containing waste alkali liquor, but also improve the impurity removal effect of rutile mother liquor and crude phosphoric acid, thereby improving the quality of ferric phosphate.

[0038] In some specific embodiments of the present invention, the method for preparing ferric phosphate specifically comprises the following steps:

[0039] S1. Add silicon-containing waste alkali solution to the rutile mother liquor to adjust the pH to 4-5, precipitate the impurity ions, separate the solid and liquid to remove Al, Ti and iron hydroxide, and add acid to the filtrate to adjust the pH to 1.8-2.0 to obtain iron salt;

[0040] S2. Add silicon-containing waste alkali solution to crude phosphoric acid to adjust the pH to 2-3, then add alkali to adjust the pH to 4.3-4.8, precipitate impurity ions, separate solid and liquid, continue to add alkali to the filtrate, adjust the pH to 6-8, and obtain phosphate salt;

[0041] S3. A precipitation reaction is carried out using iron salt, phosphate salt and hydrogen peroxide, and the solid-liquid separation is followed by washing to obtain a washed filter cake;

[0042] S4. The first-wash filter cake is slurried, phosphoric acid is added to the slurry, the temperature is increased for aging and crystallization reaction, the second-wash filter cake is obtained by washing after solid-liquid separation, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0043] In step S2, when the crude phosphoric acid is removed from impurities by using silicon-containing waste alkali liquid, after the pH is adjusted to 2-3, it is necessary to switch to conventional alkali to continue adjusting the pH to precipitate Al and Ti. Because the pH of the crude phosphoric acid is low, if the crude phosphoric acid is directly adjusted to 4.3-4.8 by using silicon-containing waste alkali liquid, the required amount of silicon-containing waste alkali liquid is large, and phosphate turbidity will appear, a large amount of silicate colloid will be generated, and filtration will be difficult. In addition, the silicon content in the obtained iron phosphate is high. In step S1, due to the relatively high pH of the mother liquor, the amount of silicon-containing waste alkali liquid required when adjusting the pH to the required pH by using silicon-containing waste alkali liquid is small, and the above problems will not occur. Therefore, in step S1, the silicon-containing waste alkali liquid can completely replace the conventional alkali liquid for impurity removal.

[0044] In some specific embodiments of the present invention, in step S1, the mass concentration of NaOH in the silicon-containing waste alkali liquid is 5%-10%, for example, it can be any point value among 5%, 6%, 7%, 8%, 9%, 10% or a range value composed of any two point values; the mass concentration of Si is 0.25%-0.5%, for example, it can be any point value among 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% or a range value composed of any two point values.

[0045] In some specific embodiments of the present invention, in step S1, the acid used includes phosphoric acid and / or sulfuric acid.

[0046] In some specific embodiments of the present invention, in step S1, the mass concentration of ferrous ions in the obtained iron salt is 40-90 g / L, for example, it can be any point value among 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L or a range value consisting of any two point values.

[0047] In some specific embodiments of the present invention, in step S2, in the crude phosphoric acid, the P2O5 content is 50wt% to 55wt%, the F content is 0.2wt% to 0.3wt%, the Fe content is 0.5wt% to 0.8wt%, the Ca content is 0 to 0.05wt%, the Mg content is 0.5wt% to 0.8wt%, the Mn content is 0 to 0.05wt%, the Al content is 0.1wt% to 0.3wt%, and the Ti content is 0.05wt% to 0.15wt%.

[0048] In some specific embodiments of the present invention, in step S2, the mass concentration of NaOH in the silicon-containing waste alkali liquid used is 10%-20%, for example, it can be any point value among 10%, 12%, 15%, 18%, 20% or a range value composed of any two point values; the mass concentration of Si is 0.5%-1%, for example, it can be any point value among 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range value composed of any two point values.

[0049] In some specific embodiments of the present invention, in step S2, the base used includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0050] In some specific embodiments of the present invention, in step S2, the mass percentage of phosphorus element in the obtained phosphate salt is 2%-4%, for example, it can be any point value among 2%, 2.5%, 3%, 3.5%, 4% or a range value consisting of any two point values.

[0051] In some specific embodiments of the present invention, in step S3, the molar ratio of Fe, P, and H2O2 in iron salt, phosphate salt and hydrogen peroxide is 1-1.3:1:0.5-1. For example, it can be any point value among 1:1:0.5, 1:1:0.75, 1:1:1, 1.2:1:0.5, 1.2:1:0.75, 1.2:1:1, 1.3:1:0.5, 1.3:1:0.75, and 1.3:1:1, or a range value consisting of any two point values.

[0052] In some specific embodiments of the present invention, in step S4, after adding phosphoric acid, the pH of the slurry is 1.4-1.6, for example, it can be any point value among 1.4, 1.5, 1.6 or a range value consisting of any two point values.

[0053] In some specific embodiments of the present invention, in step S4, the temperature of the aging crystallization reaction is 85-95°C, for example, it can be any point value among 85°C, 88°C, 90°C, 92°C, and 95°C, or a range value consisting of any two point values; the time of the aging crystallization reaction is 1-3h, for example, it can be any point value among 1h, 1.5h, 2h, 2.5h, and 3h, or a range value consisting of any two point values.

[0054] Some embodiments of the present invention are described in detail below in conjunction with specific examples. The silicon-containing waste alkali liquor used in the examples is waste alkali liquor from the zirconium industry produced during the production of zirconium oxychloride, and the remaining raw materials can be purchased from the market unless otherwise specified.

[0055] Example 1

[0056] S1. Adding NaOH with a concentration of 5wt% and a Si content of 0.25wt% zirconium waste alkali liquid to the rutile mother liquor to adjust the pH to 4.5 to precipitate the impurity ions. After solid-liquid separation, adding sulfuric acid with a mass concentration of 20wt% to the filtrate, adjusting the pH to 1.9, and obtaining an iron salt; the mass concentration of ferrous ions in the iron salt is 65g / L;

[0057] S2. Adding NaOH with a concentration of 15wt% and a Si content of 0.75wt% zirconium waste alkali liquid to crude phosphoric acid to adjust the pH to 2.5, and then adding NaOH with a mass concentration of 8wt% to adjust the pH to 4.5 to precipitate impurity ions, separate the solid and liquid, and after standing for 72h, add NaOH with a mass concentration of 32wt% to the filtrate to adjust the pH to 7 to obtain a phosphate salt; the mass percentage of phosphorus in the phosphate salt is 2.5%;

[0058] S3. A precipitation reaction was carried out using iron salt, phosphate salt and hydrogen peroxide in a molar ratio of Fe, P and H2O2 of 1:1:0.75. After a period of reaction, a solid-liquid separation and washing were performed to obtain a washed filter cake;

[0059] S4. The first-wash filter cake is slurried at 60° C., phosphoric acid with a mass concentration of 85% is added to the slurry, the pH value is adjusted to 1.5, the temperature is raised to 90° C., the slurry is kept warm for 1 hour after turning white, and the second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0060] Example 2

[0061] S1. Adding NaOH with a concentration of 8wt% and a Si content of 0.4wt% zirconium waste alkali liquid to the rutile mother liquor to adjust the pH to 4 to precipitate the impurity ions. After solid-liquid separation, adding sulfuric acid with a mass concentration of 20wt% to the filtrate, adjusting the pH to 1.8, and obtaining an iron salt; the mass concentration of ferrous ions in the iron salt is 40g / L;

[0062] S2. Adding NaOH with a concentration of 10wt% and a Si content of 0.5wt% zirconium waste alkali liquid to crude phosphoric acid to adjust the pH to 2, and then adding NaOH with a mass concentration of 8wt% to adjust the pH to 4.3, so that the impurity ions are precipitated, the solid and the liquid are separated, and after standing for 72h, adding NaOH with a mass concentration of 32wt% to the filtrate to adjust the pH to 6 to obtain a phosphate salt; the mass percentage of phosphorus in the phosphate salt is 4%;

[0063] S3. A precipitation reaction is carried out using iron salt, phosphate salt and hydrogen peroxide in a molar ratio of 1:1:1. After a period of reaction, a solid-liquid separation and washing are performed to obtain a washed filter cake;

[0064] S4. The first-wash filter cake is slurried at 60° C., phosphoric acid with a mass concentration of 85% is added to the slurry, the pH value is adjusted to 1.4, the temperature is raised to 85° C., the slurry turns white and is kept warm for 3 hours, a second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0065] Example 3

[0066] S1. Adding NaOH with a concentration of 10wt% and a Si content of 0.5wt% zirconium waste alkali liquid to the rutile mother liquor to adjust the pH to 5 to precipitate the impurity ions. After solid-liquid separation, adding sulfuric acid with a mass concentration of 20wt% to the filtrate, adjusting the pH to 2.0, and obtaining an iron salt; the mass concentration of ferrous ions in the iron salt is 90g / L;

[0067] S2. Add 20wt% NaOH and 1wt% Si content zirconium waste alkali liquid to crude phosphoric acid to adjust the pH to 3, then add 8wt% NaOH to adjust the pH to 4.8 to precipitate impurity ions, separate the solid and liquid, and add 32wt% NaOH to the filtrate after standing for 72h to adjust the pH to 8 to obtain phosphate; the mass percentage of phosphorus in the phosphate is 2%;

[0068] S3. A precipitation reaction was carried out using iron salt, phosphate salt and hydrogen peroxide in a molar ratio of 1:1:0.5. After a period of reaction, the solid-liquid separation and washing were performed to obtain a washed filter cake;

[0069] S4. The first-wash filter cake is slurried at 60° C., phosphoric acid with a mass concentration of 85% is added to the slurry, the pH value is adjusted to 1.6, the temperature is raised to 95° C., the slurry is kept warm for 1 hour after turning white, and the second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0070] Comparative Example 1

[0071] Comparative Example 1 is similar to Example 1, except that the zirconium industry waste alkali liquid with a NaOH concentration of 5wt% and a Si content of 0.25wt% in step S1 is replaced by a NaOH solution with a concentration of 5wt%, and the zirconium industry waste alkali liquid with a NaOH concentration of 15wt% and a Si content of 0.75wt% in step S2 is replaced by a NaOH solution with a concentration of 15wt%; the other process conditions are the same as those in Example 1.

[0072] Comparative Example 2

[0073] Comparative Example 2 is similar to Example 1, except that in step S2, zirconium industry waste alkali liquid with a NaOH concentration of 15wt% and a Si content of 0.75wt% is directly added to the crude phosphoric acid to adjust the pH to 4.5, and then the solid-liquid separation is performed. NaOH with a mass concentration of 8wt% is not added, and the other process conditions are the same as those in Example 1.

[0074] When zirconium industry waste alkali liquor is directly used to adjust the pH to 4.5, the phosphate becomes turbid and silicate colloid is generated, which makes extraction difficult. In addition, the Si content in the obtained iron phosphate is high, which will cause membrane scaling in subsequent water treatment.

[0075] Test example

[0076] (1) The iron phosphate prepared in Example 1 and Comparative Example 1 was tested by scanning electron microscopy. The results are as follows: Figure 1 As shown, the morphology of the iron phosphate prepared by the method of the present invention is basically consistent with that of the iron phosphate prepared by the conventional method in Comparative Example 1.

[0077] (2) The impurity contents of the iron salt, phosphorus salt and ferric phosphate obtained in each embodiment and each comparative example were respectively detected, and the specific surface area, Fe, P content and Fe / P (molar ratio) of ferric phosphate were tested. The impurity content test results are shown in Table 1, and the specific surface area, Fe, P content and Fe / P test results of ferric phosphate are shown in Table 2.

[0078] Table 1

[0079]

[0080]

[0081] Table 2

[0082]

[0083] From the above data, it can be seen that the silicon-containing waste alkali liquid generated in the production process of zirconium oxychloride is used as an impurity remover in the impurity removal and purification process of rutile mother liquor and crude phosphoric acid, and the impurity content of the obtained iron salt and phosphate salt is lower. Compared with the existing method, the use of silicon-containing zirconium industry waste alkali liquid instead of alkali liquid can not only reduce the production cost of ferric phosphate, but also improve the purification effect of iron salt and phosphate salt, reduce the impurity content of iron phosphate, and at the same time realize the reuse of silicon-containing waste alkali liquid, reducing environmental pollution and the burden of waste alkali liquid treatment.

[0084] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing ferric phosphate, characterized in that: The following steps are involved: The silicon-containing waste alkali liquid is used as an alkaline impurity remover to remove impurities from rutile mother liquor and crude phosphoric acid respectively to obtain iron salt and phosphate salt, and then the iron salt and phosphate salt are reacted with hydrogen peroxide to prepare iron phosphate.

2. The method for preparing ferric phosphate according to claim 1, characterized in that: The specific steps include: S1. Add the silicon-containing waste alkali solution to the rutile mother liquor to adjust the pH to 4-5 to precipitate the impurity ions. After solid-liquid separation, add acid to the filtrate to adjust the pH to 1.8-2.0 to obtain the iron salt; S2. Add the silicon-containing waste alkali solution to the crude phosphoric acid to adjust the pH to 2-3, then add alkali to adjust the pH to 4.3-4.8, precipitate the impurity ions, separate the solid and liquid, continue to add the alkali to the filtrate, adjust the pH to 6-8, and obtain the phosphate salt; S3. using the iron salt, the phosphate salt and the hydrogen peroxide to carry out a precipitation reaction, and washing after solid-liquid separation to obtain a washed filter cake; S4. Slurrying the first-wash filter cake, adding phosphoric acid to the slurry, heating to perform aging and crystallization reaction, washing after solid-liquid separation to obtain a second-wash filter cake, and calcining the second-wash filter cake to obtain anhydrous iron phosphate.

3. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S1, the mass concentration of NaOH in the silicon-containing waste alkali liquid is 5%-10%, and the mass concentration of Si is 0.25%-0.5%.

4. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S1, the acid includes phosphoric acid and / or sulfuric acid.

5. The method for preparing ferric phosphate according to claim 2, characterized in that: The mass concentration of ferrous ions in the iron salt is 40-90 g / L.

6. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S2, in the crude phosphoric acid, the P2O5 content is 50wt% to 55wt%, the F content is 0.2wt% to 0.3wt%, the Fe content is 0.5wt% to 0.8wt%, the Ca content is 0 to 0.05wt%, the Mg content is 0.5wt% to 0.8wt%, the Mn content is 0 to 0.05wt%, the Al content is 0.1wt% to 0.3wt%, and the Ti content is 0.05wt% to 0.15wt%.

7. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S2, the mass concentration of NaOH in the silicon-containing waste alkali liquid is 10%-20%, and the mass concentration of Si is 0.5%-1%.

8. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S2, the alkali includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

9. The method for preparing ferric phosphate according to claim 2, characterized in that: In step S2, the mass percentage of phosphorus element in the phosphorus salt is 2%-4%.

10. The method for preparing ferric phosphate according to claim 2, characterized in that: Contains at least one of the following characteristics: (1) In step S3, the molar ratio of Fe, P, and H2O2 in the iron salt, the phosphate salt, and the hydrogen peroxide is 1-1.3:1:0.5-1; (2) In step S4, after adding the phosphoric acid, the pH of the slurry is 1.4-1.6; (3) In step S4, the temperature of the aging crystallization reaction is 85-95° C., and the time of the aging crystallization reaction is 1-3 h.

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